/*
 * Copyright 2015 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */

/*
 * Copyright 2014 Twitter, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package io.netty.handler.codec.http2;

import io.netty.util.AsciiString;
import io.netty.util.internal.ConstantTimeUtils;
import io.netty.util.internal.PlatformDependent;

final class HpackUtil {
    /**
     * Compare two {@link CharSequence} objects without leaking timing information.
     * <p>
     * The {@code int} return type is intentional and is designed to allow cascading of constant time operations:
     * <pre>
     *     String s1 = "foo";
     *     String s2 = "foo";
     *     String s3 = "foo";
     *     String s4 = "goo";
     *     boolean equals = (equalsConstantTime(s1, s2) & equalsConstantTime(s3, s4)) != 0;
     * </pre>
     * @param s1 the first value.
     * @param s2 the second value.
     * @return {@code 0} if not equal. {@code 1} if equal.
     */
    static int equalsConstantTime(CharSequence s1, CharSequence s2) {
        if (s1 instanceof AsciiString && s2 instanceof AsciiString) {
            if (s1.length() != s2.length()) {
                return 0;
            }
            AsciiString s1Ascii = (AsciiString) s1;
            AsciiString s2Ascii = (AsciiString) s2;
            return PlatformDependent.equalsConstantTime(s1Ascii.array(), s1Ascii.arrayOffset(),
                                                        s2Ascii.array(), s2Ascii.arrayOffset(), s1.length());
        }

        return ConstantTimeUtils.equalsConstantTime(s1, s2);
    }

    /**
     * Compare two {@link CharSequence}s.
     * @param s1 the first value.
     * @param s2 the second value.
     * @return {@code false} if not equal. {@code true} if equal.
     */
    static boolean equalsVariableTime(CharSequence s1, CharSequence s2) {
        return AsciiString.contentEquals(s1, s2);
    }

    // Section 6.2. Literal Header Field Representation
    enum IndexType {
        INCREMENTAL, // Section 6.2.1. Literal Header Field with Incremental Indexing
        NONE,        // Section 6.2.2. Literal Header Field without Indexing
        NEVER        // Section 6.2.3. Literal Header Field never Indexed
    }

    // Appendix B: Huffman Codes
    // https://tools.ietf.org/html/rfc7541#appendix-B
    static final int[] HUFFMAN_CODES = {
            0x1ff8,
            0x7fffd8,
            0xfffffe2,
            0xfffffe3,
            0xfffffe4,
            0xfffffe5,
            0xfffffe6,
            0xfffffe7,
            0xfffffe8,
            0xffffea,
            0x3ffffffc,
            0xfffffe9,
            0xfffffea,
            0x3ffffffd,
            0xfffffeb,
            0xfffffec,
            0xfffffed,
            0xfffffee,
            0xfffffef,
            0xffffff0,
            0xffffff1,
            0xffffff2,
            0x3ffffffe,
            0xffffff3,
            0xffffff4,
            0xffffff5,
            0xffffff6,
            0xffffff7,
            0xffffff8,
            0xffffff9,
            0xffffffa,
            0xffffffb,
            0x14,
            0x3f8,
            0x3f9,
            0xffa,
            0x1ff9,
            0x15,
            0xf8,
            0x7fa,
            0x3fa,
            0x3fb,
            0xf9,
            0x7fb,
            0xfa,
            0x16,
            0x17,
            0x18,
            0x0,
            0x1,
            0x2,
            0x19,
            0x1a,
            0x1b,
            0x1c,
            0x1d,
            0x1e,
            0x1f,
            0x5c,
            0xfb,
            0x7ffc,
            0x20,
            0xffb,
            0x3fc,
            0x1ffa,
            0x21,
            0x5d,
            0x5e,
            0x5f,
            0x60,
            0x61,
            0x62,
            0x63,
            0x64,
            0x65,
            0x66,
            0x67,
            0x68,
            0x69,
            0x6a,
            0x6b,
            0x6c,
            0x6d,
            0x6e,
            0x6f,
            0x70,
            0x71,
            0x72,
            0xfc,
            0x73,
            0xfd,
            0x1ffb,
            0x7fff0,
            0x1ffc,
            0x3ffc,
            0x22,
            0x7ffd,
            0x3,
            0x23,
            0x4,
            0x24,
            0x5,
            0x25,
            0x26,
            0x27,
            0x6,
            0x74,
            0x75,
            0x28,
            0x29,
            0x2a,
            0x7,
            0x2b,
            0x76,
            0x2c,
            0x8,
            0x9,
            0x2d,
            0x77,
            0x78,
            0x79,
            0x7a,
            0x7b,
            0x7ffe,
            0x7fc,
            0x3ffd,
            0x1ffd,
            0xffffffc,
            0xfffe6,
            0x3fffd2,
            0xfffe7,
            0xfffe8,
            0x3fffd3,
            0x3fffd4,
            0x3fffd5,
            0x7fffd9,
            0x3fffd6,
            0x7fffda,
            0x7fffdb,
            0x7fffdc,
            0x7fffdd,
            0x7fffde,
            0xffffeb,
            0x7fffdf,
            0xffffec,
            0xffffed,
            0x3fffd7,
            0x7fffe0,
            0xffffee,
            0x7fffe1,
            0x7fffe2,
            0x7fffe3,
            0x7fffe4,
            0x1fffdc,
            0x3fffd8,
            0x7fffe5,
            0x3fffd9,
            0x7fffe6,
            0x7fffe7,
            0xffffef,
            0x3fffda,
            0x1fffdd,
            0xfffe9,
            0x3fffdb,
            0x3fffdc,
            0x7fffe8,
            0x7fffe9,
            0x1fffde,
            0x7fffea,
            0x3fffdd,
            0x3fffde,
            0xfffff0,
            0x1fffdf,
            0x3fffdf,
            0x7fffeb,
            0x7fffec,
            0x1fffe0,
            0x1fffe1,
            0x3fffe0,
            0x1fffe2,
            0x7fffed,
            0x3fffe1,
            0x7fffee,
            0x7fffef,
            0xfffea,
            0x3fffe2,
            0x3fffe3,
            0x3fffe4,
            0x7ffff0,
            0x3fffe5,
            0x3fffe6,
            0x7ffff1,
            0x3ffffe0,
            0x3ffffe1,
            0xfffeb,
            0x7fff1,
            0x3fffe7,
            0x7ffff2,
            0x3fffe8,
            0x1ffffec,
            0x3ffffe2,
            0x3ffffe3,
            0x3ffffe4,
            0x7ffffde,
            0x7ffffdf,
            0x3ffffe5,
            0xfffff1,
            0x1ffffed,
            0x7fff2,
            0x1fffe3,
            0x3ffffe6,
            0x7ffffe0,
            0x7ffffe1,
            0x3ffffe7,
            0x7ffffe2,
            0xfffff2,
            0x1fffe4,
            0x1fffe5,
            0x3ffffe8,
            0x3ffffe9,
            0xffffffd,
            0x7ffffe3,
            0x7ffffe4,
            0x7ffffe5,
            0xfffec,
            0xfffff3,
            0xfffed,
            0x1fffe6,
            0x3fffe9,
            0x1fffe7,
            0x1fffe8,
            0x7ffff3,
            0x3fffea,
            0x3fffeb,
            0x1ffffee,
            0x1ffffef,
            0xfffff4,
            0xfffff5,
            0x3ffffea,
            0x7ffff4,
            0x3ffffeb,
            0x7ffffe6,
            0x3ffffec,
            0x3ffffed,
            0x7ffffe7,
            0x7ffffe8,
            0x7ffffe9,
            0x7ffffea,
            0x7ffffeb,
            0xffffffe,
            0x7ffffec,
            0x7ffffed,
            0x7ffffee,
            0x7ffffef,
            0x7fffff0,
            0x3ffffee,
            0x3fffffff // EOS
    };

    static final byte[] HUFFMAN_CODE_LENGTHS = {
            13, 23, 28, 28, 28, 28, 28, 28, 28, 24, 30, 28, 28, 30, 28, 28,
            28, 28, 28, 28, 28, 28, 30, 28, 28, 28, 28, 28, 28, 28, 28, 28,
            6, 10, 10, 12, 13, 6, 8, 11, 10, 10, 8, 11, 8, 6, 6, 6,
            5, 5, 5, 6, 6, 6, 6, 6, 6, 6, 7, 8, 15, 6, 12, 10,
            13, 6, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
            7, 7, 7, 7, 7, 7, 7, 7, 8, 7, 8, 13, 19, 13, 14, 6,
            15, 5, 6, 5, 6, 5, 6, 6, 6, 5, 7, 7, 6, 6, 6, 5,
            6, 7, 6, 5, 5, 6, 7, 7, 7, 7, 7, 15, 11, 14, 13, 28,
            20, 22, 20, 20, 22, 22, 22, 23, 22, 23, 23, 23, 23, 23, 24, 23,
            24, 24, 22, 23, 24, 23, 23, 23, 23, 21, 22, 23, 22, 23, 23, 24,
            22, 21, 20, 22, 22, 23, 23, 21, 23, 22, 22, 24, 21, 22, 23, 23,
            21, 21, 22, 21, 23, 22, 23, 23, 20, 22, 22, 22, 23, 22, 22, 23,
            26, 26, 20, 19, 22, 23, 22, 25, 26, 26, 26, 27, 27, 26, 24, 25,
            19, 21, 26, 27, 27, 26, 27, 24, 21, 21, 26, 26, 28, 27, 27, 27,
            20, 24, 20, 21, 22, 21, 21, 23, 22, 22, 25, 25, 24, 24, 26, 23,
            26, 27, 26, 26, 27, 27, 27, 27, 27, 28, 27, 27, 27, 27, 27, 26,
            30 // EOS
    };

    static final int HUFFMAN_EOS = 256;

    private HpackUtil() {
        // utility class
    }
}
